I've heard recently of another completely wacky theory... The fact that the Earth isn't exactly flat, but laid out almost flat on a huge, HUGE ice ball around which the sun orbits because at night it flies through a tunnel in the ice ball. And they suppose that there are other worlds somewhere on the ice ball.
Let them a couple years and they'll come up with the idea that the Earth is flat, but just stuck on a sphere that happens to be of the exact right shape and size for the planet to wrap itself around!

same as above, but also a sphere version. Something like, earth is 1000x larger than we're taught and so that's why it feels flat. and there's many many more continents out there besides the ones we know.